The C125N35AFM is a 3-pole ComPacT NS new generation molded-case circuit breaker from Schneider Electric, rated 1250 A at 50 °C. That 1250 A figure is the trip-unit rating (In), not the frame rating — the breaker's continuous current capacity at the listed ambient. The MicroLogic 5.0 A electronic trip unit provides LSI protection: long-time (L) for overload, short-time (S) for selective short-circuit coordination, and instantaneous (I) for high-fault clearing. This is a distribution-grade breaker (EN/IEC 60947-2, utilization category B), meaning it's designed for main or feeder protection in low-voltage switchboards, not for direct motor starting. The breaking capacity is the headline selector: 85 kA Icu at 220/240 V AC, 50 kA at 380/415 V, 40 kA at 500/525 V, and 30 kA at 660/690 V. The 85 kA at 240 V matters for North American 277/480 V wye systems where the line-to-neutral fault current can be high. The Icu (ultimate breaking capacity) is the maximum fault the breaker can clear once; the Ics (service breaking capacity, not listed here but typically 50–100% of Icu per IEC 60947-2) governs how many operations it survives. For a main breaker where fault duty is known and coordination is designed, the Icu is the binding spec. The MicroLogic 5.0 A trip unit is electronic, not thermal-magnetic, so it offers adjustable long-time, short-time, and instantaneous pickups plus a thermal-memory function (20-minute reset time). That adjustability is what lets the commissioning engineer set selective coordination with downstream breakers — the short-time delay can be tuned to ride through inrush without nuisance tripping. The LCD display shows real-time current (ammeter function), and the four red LEDs indicate fault type (overload, short-circuit, etc.), which speeds troubleshooting on a live panel.
Fixed-mount design on a backplate (not draw-out). Dimensions: 327 mm high, 210 mm wide, 147 mm deep. Front-connect both upstream and downstream — no rear-access required, which simplifies panel layout and busbar routing. IK07 impact rating confirms it survives a 2 J hammer blow (typical for panel-mounted gear).
Overvoltage category III (fixed installation, not plug-in). No earth-leakage protection integrated (the MicroLogic 5.0 A is LSI only; add a Vigi module for ground-fault).